Referring to FIG. 10, a conventional pet house made of paper includes a house-shaped box 90 and a roof 92. The house-shaped box 90 includes a front wall 93, a rear wall 94 and two lateral walls 95. The front wall 93 defines a door 96. Each of the lateral walls 95 defines a plurality of windows 91. The front wall 93 and the rear wall 94 both include a triangular upper portion on which the roof 92 is mounted. However, as shown, the roof 92 is very likely to deform because of its own weight and lack of support in the middle.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.